1. Field of the Invention
The present invention, in general relates to casters and, more particularly, to casters that are adapted for use on irregular surfaces.
Prior U.S. Pat. No. 5,507,069 that issued on Apr. 16, 1996, to the same inventor describes a related type of articulated caster and its disclosure and contents are included herein by reference.
There is a need for casters to support and move objects over varying types of terrain. Even concrete floors have small irregularities in the surface that casters must pass over. These irregularities are substantial for the wheels of a caster to overcome when there is a heavy load on the caster.
The prior patent, mentioned hereinabove, discloses a unique mechanism by which a caster's trailing wheels can, at times, lag behind each other and in so doing rise up over obstacles.
While this represents a substantial improvement in casters, there still remain certain unsatisfied needs. For example, there is a need for a simple and effective braking mechanism for use with a caster.
Previous braking methods that apply friction to a wheel of a caster are ineffective if there is a low coefficient of friction intermediate the wheel and the surface upon which the wheel is placed. This is because such a strategy for braking relies upon friction between a wheel and the surface to prevent movement of the object being supported.
Also, there is no way to vary the coefficient of friction at the interface between the wheel and the surface. By definition, the wheels of a caster must be durable. This generally translates into hard wheels, especially when heavy loads are carried. Hard wheels (steel, certain types of plastics, etc.) that can carry heavy loads tend to have a relatively low coefficient of friction. This is the opposite of what is desired.
Often, the object being supported must be retained not only in place, but it must be prevented from moving at all with respect to the surface. Attempting to supply a brake force directly to a caster's wheel to prevent rotation of the wheel introduces play, even when the wheel is a non-pivoting fixed-direction type of caster.
When the caster is adapted to pivot (for steering purposes), there is substantial movement that can occur even with a “locked” wheel allowing the wheel to stay in position on the ground and pivot about a circle. This results in considerable movement of the payload.
Also, there is a long standing need to positively engage the braking effect of a caster when desired and to positively remove the braking effect when it is not desired. The braking mechanisms of certain prior types of caster design do not totally engage or disengage. Consequently, a user may think a brake is fully applied when, in fact, it has only been partially applied. Conversely, a user may think a brake is fully disengaged when, in fact, it is only partially disengaged. This problem is also further aggravated by the fact that most users are unable to determine which direction a braking lever adjacent to a wheel of a caster is urged for braking. Consequently, the user may think he has removed the braking from all four casters (on at each of four corners is typical for most objects) when, in fact, the braking mechanism remains engages for one or more of the casters. This makes movement of the object difficult to accomplish. Conversely, when the user thinks he has applied the braking force to all four casters and when some of them are not engaged, the object (i.e., the load or cargo) may begin to move and “run away” from the user once it is released.
Also, all brakes wear. With certain prior types of casters, this means the braking force decreases with age as the braking mechanism wears.
Furthermore, stopping a wheel of the caster from rotating is a poor solution at braking the load. The caster's wheels are typically hard and have a low coefficient of friction intermediate the wheel and the surface upon which the wheel is to be used. A high coefficient of friction wheel tends to be a soft wheel that wears quickly and is, therefore, either not used or available with casters that are intended to support heavy loads.
Furthermore, when the wheel is used to brake a caster, there is no way to vary the coefficient of friction intermediate the caster and the surface upon which the caster is used.
Also floors, as mentioned hereinabove, are irregular. If an attempt is made to apply a braking force from the caster directly to a surface underneath the caster, it is desirable to accommodate fluctuations in the distance the floor is disposed below the caster.
Also, it is desirable to be able to safely apply a caster brake while in motion without risk of injury, for example, the caster running over the foot of the user.
Prior art designs also shift the center of gravity of an applied load when the caster changes direction.
Accordingly, there is a need for a braking caster that overcomes these prior limitations.
Also, while the benefits of the caster that is disclosed in the prior mentioned patent application are substantial, there are disadvantages associated with its design. For example, the ball and socket assembly that it utilizes is difficult to manufacture and, therefore, expensive. It is time-consuming to assemble.
There is also a potential weakness at the point of connection immediately above the pivot ball that tends to limit the maximum amount of force (i.e., load) that can be accomplished.
Also, the ball and socket assembly requires structures that can support both the ball and the socket which tend to limit the range of caster applications that can utilize such a design.
It is desirable to provide a stronger joint that has the additional benefits of being less expensive to manufacture and easier to assembly as well as adapted for use, including retrofit, into a variety of existing caster applications.
It is also desirable to provide an articulated caster that can be used in plurality to form a compound carriage system that is adapted to support a payload without a need to excessively elevate the payload.
Accordingly, there exists today a need for an articulated caster that can help ameliorate the aforementioned difficulties.
Clearly, such an apparatus would be a useful and desirable device.
2. Description of Prior Art
Casters are, in general, known. For example, the following patents describe various types of these devices:
U.S. Pat. No. 5,507,069 to Willis, Apr. 16, 1996;
U.S. Pat. No. 301,925 to Roux, Jul. 15, 1884;
U.S. Pat. No. 344,988 to Richmond, Jul. 6, 1886;
U.S. Pat. No. 1,622,447 to Kalberer, Mar. 29, 1927;
U.S. Pat. No. 1,666,139 to Johnson, Apr. 17, 1928;
U.S. Pat. No. 2,123,707 to Bloch, Jul. 12, 1938;
U.S. Pat. No. 3,433,500 to Christensen, Mar. 18, 1969;
U.S. Pat. No. 4,053,129 to Graff, Oct. 11, 1977; and
U.K. Patent No. 4822 to Kendrick's, Dec. 18, 1877.
While the structural arrangements of the above described devices, at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.